Mirror - Some of the bullets aren't spawning correctly. It isn't random, but instead comes in "batches". I'm guessing it is hitting the bullet cap limit. You can tell by watching the MirrorShotUp/Down and how it acts when it bounces. Frequently the shots disappear on the bounce, sometimes intermittently and sometimes in large swathes.
....bah! I'll be honest, I'm starting to dislike this boss. Like the bloody Obscura Disc in TLF, I hated that thing too.
It shouldnt be hitting any sort of cap though, that's for sure; I wasnt even aware the game HAD one. Originally Battleswarm's 2nd pattern put out waaaaaaaayyyyyyyyyy more bullets than it does now (at least twice as much, probably more), and as far as I could tell, there isnt any cap, but there IS a point at which the framerate starts to get wonky, which is why the pattern was altered to prevent that from happening (mostly). I mean, really, bullet count was downright absurd. I assume it was a good idea at the time.
I *think* I know what you mean as for the problems with this boss right now though, and I sorta kinda think I have an idea as to what it might be, I'll have to go have a look at it more closely.
